The present invention is directed to a process for the preparation of iminodiacetonitrile (IDAN) and iminodiacetic acid (IDA) and derivatives thereof.
It is well known that IDAN is a valuable intermediate to prepare compounds such as IDA. It is also well known that IDA is a valuable intermediate for the preparation of other compounds. In fact, IDA is produced in commercial quantities in the United States for use as an intermediate in the preparation of numerous other compounds. Numerous methods are known in the art to prepare both IDAN and IDA.
For example, U.S. Pat. No. 3,886,198 to Philbrook, et al., discloses a process for preparing IDAN by preparing an aqueous mixture of hexamethylenetetramine, hydrogen cyanide and a strong acid such as sulfuric acid, hydrochloric acid and nitric acid, the aqueous mixture having a pH of 3 to 5 and a mole ratio of hexamethylenetetramine to hydrogen cyanide of 1 to 5-7. The aqueous mixture is passed through a tubular reactor reaction zone at a temperature between 50.degree. C. and 120.degree. C.
U.S. Pat. No. 3,988,360 to Gaudette, et al., discloses a continuous process for preparing IDAN by continuously preparing an aqueous reaction mixture of hexamethylenetetramine, formaldehyde and hydrogen cyanide having a mole ratio of hexamethylenetetramine to formaldehyde to hydrogen cyanide of 1 to 1-2.2 to 6.9-8.6 in a continuous reaction zone by continuously feeding an aqueous hexamethylenetetramine solution having a temperature of 0.degree.-80.degree. C., an aqueous formaldehyde solution having a temperature of 0.degree.-80.degree. C., and hydrogen cyanide having a temperature of 0.degree.-25.degree. C. into a continuous reaction zone at a temperature between 50.degree. and 250.degree. C. The pH of the resulting aqueous reaction mixture is between 5 and 10. The resulting IDAN can be recovered, or it can be hydrolyzed to form an alkali metal salt of IDA, which can be recovered or converted to IDA by acidification.
U.S. Pat. No. 4,307,037 to Suchsland, et al., discloses a process for the production of IDAN by reaction of hexamethylenetetramine with hydrogen cyanide in acidic aqueous mediums. In the process, the pH during the reaction is between 5.5 and 7.5 at the beginning, and is progressively lowered during the reaction by about 0.5 to 3.5 units by the addition of acid.
United States Statutory Invention Registration H4 to Cullen discloses a process for preparing IDAN by the reaction of 1 mole equivalent of hexamethylenetetramine, 2 mole equivalents of formaldehyde, and 8 mole equivalents of hydrogen cyanide at a temperature between about 20.degree. and 90.degree. C. and at a pH between 5.5 and 6.5.
Although satisfactory results can be achieved by these prior art processes, all of them suffer from one or more disadvantages. All of the prior art processes produce unwanted by-products such as glycolonitrile, aminoacetonitrile, ammonium salts, and the like. Now, there is provided an improvement to the prior art processes which converts most of the by-products to the desired IDAN, IDA, and derivatives thereof, and increases the overall yields. Because the quantity of the by-products is reduced, disposal of these by-products is significantly simplified.